1. Field of the Invention
The present invention relates to a method and apparatus for selecting an antenna in a communication system. More particularly, the present invention relates to a method and apparatus for selecting a transmit antenna in an orthogonal frequency division multiple access (OFDMA) communication system employing a beamforming-multiple input multiple output (MIMO) scheme (hereinafter referred to as “beamforming-MIMO/OFDMA communication system”).
2. Description of the Related Art
Next-generation communication systems are evolving with an emphasis on being able to transmit/receiving high-capacity data to/from a plurality of mobile stations (MS) at high speed. In order to achieve high-speed and high-capacity data transmission, it is important for next-generation communication systems to increase a data transfer rate and improve transmission reliability. Most next-generation communication systems use a MIMO scheme as a scheme for increasing a data transfer rate and improving transmission reliability. The MIMO scheme is a scheme in which a base station (BS) and a mobile station (MS) are provided with a plurality of antennas respectively, and transmit/receive data through their antennas. The MIMO scheme overcomes bandwidth resource limitations in a frequency domain by making the most of a space domain.
In a communication system using the MIMO scheme, each channel generated by each antenna has a spatial correlation with each of other channels, and the communication system suffers from a significant decrease in data transfer rate and a lowering of transmission reliability due to the spatial correlation between the respective channels. A two-dimensional transmit beamforming scheme using a spatial correlation matrix has been proposed to overcome such a problem.
The two-dimensional transmit beamforming scheme is a transmit beamforming scheme combined with a space-time block code (STBC), which uses an eigen-vector and an eigen-value of a spatial correlation matrix. Thus, a communication system using the two-dimensional transmit beamforming scheme can produce a space diversity effect through the STBC, and can reduce loss according to a spatial correlation between channels through the transmit beamforming scheme.
However, in a communication system using the two-dimensional transmit beamforming scheme, there is a problem in that a BS cannot obtain a sufficient diversity gain achievable by multiple transmit/receive antennas because it receives only statistical channel information and uses the received statistical channel information so as to reduce the effect of a spatial correlation between communication channels. For example, if a BS uses 4 antennas and the two-dimensional transmit beamforming scheme, and an MS uses one antenna, then only a second-order transmit diversity gain can be obtained despite there being a maximum of a fourth-order transmit diversity gain.
As a scheme for improving communication system performance by maximizing a transmit diversity gain, a communication has been proposed, in which the STBC is combined with a transmit antenna selection scheme. In a communication system using the STBC, an increase in transmit diversity gain generally results in a decrease in data transfer rate. To compensate for this, a communication system has been created, which can increase a transmit diversity gain without a decrease in data transfer rate by using the STBC and the transmit antenna selection scheme.
Hereinafter, the transmit antenna selection scheme will be described in more detail. In the transmit antenna selection scheme, an MS calculates a signal-to-noise ratio (SNR) corresponding to a received signal of each receive antenna, estimated in the MS, and selects at least two transmit antennas with the largest SRN to thereby generate antenna selection information. Also, the MS feeds back the antennas selection information to a BS. Subsequently, the BS selects a corresponding transmit antenna from among transmit antennas by using the antennas selection information, and transmits a space-time block coded signal to the MS through the selected transmit antenna.
However, since a communication system using the transmit antenna selection scheme allows for a transmit diversity gain, but does not take into account a spatial correlation between channels, there is a problem in that the performance of the communication system is lowered when there is a large spatial correlation between channels.